On the approximation exponent of some hyperquadratic power series

In this paper, we give the value of the approximation exponent of the hyperquadratic power series satisfying the equation $$Cx^{r}-Ax^{r-1}-1=0$$ where $r> 2$ is a power of a prime number $p$, $A$ and $C$ are nonzero polynomials over a finite field $\mathbf{K}$ of characteristic $p$ and $\deg A> \deg C$. Further, we exhibit explicitly its continued fraction expansion when $C$ divides $A$.